This invention relates to gas separation, in particular to an air separation plant.
An air separation plant is often provided with a product compressor in addition to one or more air compressors. In large plants producing more than 1000 tonnes per day of product, separation is normally performed by rectification.
U.S. Pat. No. 4,382,366 relates to an air separation plant which produces an oxygen product. An oxygen product compressor is directly driven by a steam turbine. A waste nitrogen stream containing sufficient oxygen to support combustion is taken from the rectification column in which the oxygen product is separated and is without further compression introduced into a chamber in which combustion of a fuel gas takes place. The resultant combustion products are expanded in a turbo-expander. The steam supplied to the steam turbine is raised by heat exchange with the combustion gases exhausted from the turbo-expander. The oxygen product compressor, the air compressor of the air separation plant, the steam turbine and the turbo-compressor are all coupled together. Such a plant cannot produce nitrogen in large quantities.
The largest plants may produce up to 10,000 tonnes per day of product nitrogen at elevated pressure. Accordingly, large product nitrogen compressors are required. Conventionally, such compressors are driven by electrical motors. The electrical motors are often large and problems can arise in starting up the motors. Typically additional start-up motors are provided.
It is the aim of the present invention to provide an air separation plant which does not require an electrical motor for the purposes of driving a product nitrogen compressor.